Electric motors and their control systems commonly used for, such as, various mechanical, industrial, automobile applications. Example of those applications, especially for involving variable frequency drive for electric motors, include hybrid vehicles and variable speed applications for appliances and HVAC (e.g., heating, ventilation, and air conditioning) systems. As an illustrative example, many conventional electric motor control systems use induction-type, synchronous motors and open-loop voltage/frequency (V/Hz) control techniques to control motors. Due to efficiency considerations, more and more permanent magnet synchronous motors (PMSMs) are replacing induction-type, synchronous motors in various applications. Compared to induction motors, PMSMs are also capable of providing higher power density with a smaller size.
In PMSM systems, conventional open-loop voltage/frequency control techniques may be inferior, because they tend to cause unstable vibrations, which may be caused by the small damping between the rotor and the stator of the PMSMs.
Therefore, it may be desirable to provide alternative control systems and methods for controlling PMSMs.